It happened around 5 p.m. Tuesday in Philadelphia's Kensington section.
Police say the 43-year-old man was walking to prayer service with another man when the gunfire erupted.
"You can clearly see our victim walking to this mosque for a prayer service. He was walking with another male. You see the shooter run up behind the victim, and from just a few feet away, begin firing shots," said Philadelphia Police Chief Inspector Scott Small.
Video reportedly shows the victim collapsing in the parking lot. Police say the gunman then stood over the man and kept firing execution-style.
A total of 17 shots were fired in the incident, according to Small.
The victim suffered a gunshot wound to the head and multiple gunshot wounds to the torso. He was rushed to an area hospital where he was pronounced dead.
Police provide update on deadly shooting outside mosque
Chopper 6 with our sister station, 6ABC Action News in Philadelphia, was overhead as officers cordoned off the parking lot, which is located near the Al-Aqsa Islamic Society along Germantown Avenue.
No arrests have been made and no weapons were recovered.
Police say no other injuries were reported.
The suspect was last seen fleeing on foot before jumping into a dark-colored sedan.
Anyone with information is asked to call police at 215-686-TIPS.